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| Liquid sulfur trioxide |
Sulfur trioxide having monomeric and polymeric forms in liquid and gas state respectively.
It is produced by the heating of oleum followed by condensation process.
In this process produced liquid SO3 having traces of sulfuric acid.
Sulfuric acid enters into sulfur trioxide during heating of oleum.
Heating at higher temperature than oleum boiling point causes sulfuric acid enters into liquid sulfur trioxide.
A lab result of liquid sulfur trioxide gives us pure SO3 % content in the sample. Other than SO3 content remaining is sulfuric acid as residue.
This sulfuric acid molecule provides additional bonding between SO3 molecules & make it low melting SO3.
Sulfur trioxide molecules come together with additional bonding caused by sulfuric acid molecules.
We will calculate how much amount of sulfuric acid forms low melting of SO3?
For 1 ton of SO3 content it lab result is 99.51% of pure SO3 & remaining as acid content.
Pure SO3 content = 995.1 kg = 12.44 Kmol
1 mol = total 6.023E+23 molecules
1 kmol = total 6.023E+26 molecules
Total SO3 molecules = (12.44 kmol) ✖ (6.023E+23) = 7.49E+27 molecules
Considering S3O9 forms of Liquid SO3
Total S3O9 molecules = (7.49E+27 / 3) = 2.50E+27 molecules
SO3 hydrogen bond acceptor count = 3
H2SO4 content in SO3 sample = 0.49 % of total SO3 = 4.9 kg = 0.05 kmol
1 mol = total 6.023E+23 molecules
1 kmol = total 6.023E+26 molecules
Total H2SO4 molecules = (0.05 kmol) ✖ (6.023E+23) = 3.01E+25 molecules
Total additional bonds created with sulfuric acid content
= 3.01E+25
A typical bonding between S3O9 form create 1 poly molecule shown below.
S3O9-------S3O9-------S3O9-------S3O9
Total poly molecules will be created = (3.01E+25) / 3 = 1.00E+25 poly molecules
1 poly molecule has 4 S3O9 molecule
So, total S3O9 molecules take participate in poly molecule will be
= (1.00E+25) ✖ 4
= 4.02E+25 S3O9 molecules take participate in creating poly molecules
= (4.02E+25) ✖ 3
= 1.20E+26 SO3 molecules take participate in creating poly molecules
= (1.20E+26) / (6.023E+26)
= 0.20 kmol of SO3
= 0.20 ✖ 80
= 16 kg of SO3
So, Total 16 kg of SO3 out of total 1 ton of liquid So3 having 99.51 % of pure SO3 will be of low melting.
This change can’t be observed in continuous process.
Temperature cycle & residence time could be effect on formation of low melting So3.
This is the simple calculation based on hypothetical concept of bonding between molecules.
This is all hypothetical calculation. It may be not meet with the real experimental data, but this calculation or fundamentals give us an opportunity to think further on this topic.
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